Airless tire construction having variable stiffness

ABSTRACT

An airless tire has a wheel portion and a webbing extending from the wheel portion towards an axis of rotation of the airless tire. The stiffness of the webbing varies along an axial direction of the airless tire. The diameter of an annular outer surface of the wheel portion varies along an axial direction of the airless tire.

FIELD OF INVENTION

The present disclosure relates to an airless tire. More particularly,the present disclosure relates to an airless tire having varyingattributes.

BACKGROUND

Airless, or non-pneumatic tires known in the art include spokes or spokerings each having the same stiffness and the same diameter. These priorart spokes buckle or deflect upon contact with the ground, and create acontact patch shape with substantially straight leading and trailingedges. These prior art spokes may be constructed of a material that isrelatively stronger in tension than in compression, such that when thelower spokes buckle, the load can be distributed through the remainingportion of the wheel.

SUMMARY

In one embodiment, an airless tire comprises one or more spoke ringsadjacent to one another, with each spoke ring having spokes extendingfrom inner and outer annular surfaces of each spoke ring. At least oneof the spoke rings has a different stiffness than another spoke ring. Atread layer extends circumferentially around the annular outer surfacesof the spoke rings.

In another embodiment, a tire is made of webbing extending from anannular inner surface of a wheel portion of the tire. The webbingextends towards an axis of rotation of the tire. The tire includes awheel portion with an annular outer surface, which varies in diameteralong an axial direction of the tire. The stiffness of the webbing alsovaries along an axial direction of the tire.

In yet another embodiment, a tire includes at least three spoke ringsadjacent to one another. Two of the spoke rings have approximately equalstiffnesses, which are different from the stiffness of the other spokering. Each spoke ring further comprises a plurality of spokes extendingbetween inner and outer annular surfaces of each spoke ring. A treadlayer extends circumferentially around the spoke rings to providetraction with a surface.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings, structures are illustrated that, togetherwith the detailed description provided below, describe exemplaryembodiments of the claimed invention. Like elements are identified withthe same reference numerals. It should be understood that elements shownas a single component may be replaced with multiple components, andelements shown as multiple components may be replaced with a singlecomponent. The drawings are not to scale and the proportion of certainelements may be exaggerated for the purpose of illustration.

FIG. 1 is a schematic drawing showing a perspective view of oneembodiment of an airless tire 100 having multiple spoke rings;

FIG. 2 is a schematic drawing illustrating a cross-section of theairless tire 100;

FIG. 3 is a schematic drawing illustrating a cross-section of analternative embodiment of an airless tire having multiple spoke rings ofvarying diameter, stiffness, and thickness;

FIG. 4 is a schematic drawing illustrating a cross-section of anotheralternative embodiment of an airless tire having multiple spoke rings ofvarying diameter, stiffness, and thickness, with each spoke ring havingconvex and concave portions;

FIG. 5 is a perspective view of still another alternative embodiment ofan airless tire, having a unitary wheel portion and webbing;

FIG. 6 is a schematic drawing illustrating an exemplary rounded contactpatch shape made by an airless tire, where the contact patch shape has arounded leading edge and a rounded trailing edge;

FIG. 7 is a schematic drawing illustrating an exemplary contact patchshape of a prior art tire, where the footprint has a flat leading edgeand a flat trailing edge; and

FIG. 8 is a schematic drawing illustrating a side view of the airlesstire 100 bearing a load.

DETAILED DESCRIPTION

The following includes definitions of selected terms employed herein.The definitions include various examples or forms of components thatfall within the scope of a term and that may be used for implementation.The examples are not intended to be limiting. Both singular and pluralforms of terms may be within the definitions.

“Axial” and “axially” refer to a direction that is parallel to the axisof rotation of a tire.

“Circumferential” and “circumferentially” refer to a direction extendingalong the perimeter of the surface of the tread perpendicular to theaxial direction.

“Equatorial plane” refers to the plane that is perpendicular to thetire's axis of rotation and passes through the center of the tire'stread.

“Tread” refers to that portion of the tire that comes into contact withthe road under normal inflation and load.

FIG. 1 illustrates one embodiment of an airless tire 100 having an axisof rotation A passing through its center. Airless tire 100 isconstructed of five spoke rings 110, including a central spoke ring 110a, a pair of intermediate spoke rings 110 b disposed on each side of thecentral spoke ring 110 a, and a pair of outer spoke rings 110 c disposedon either side of intermediate spoke rings 110 b. Each of the spokerings 110 includes a plurality of spokes 112. While five spoke rings areshown in the illustrated embodiment, it should be understood that theairless tire 100 is not limited to any particular number of spoke rings,and may alternatively utilize structures other than spoke rings, such asa unitary structure having a plurality of spokes. The spoke rings 110may be constructed of materials including, without limitation, cordedcarbon-filled rubber, nylon, polyester, fibers (glass, aramid, etc.)with resin, thermoplastic, or urethane.

Each spoke ring 110 each has an inner annular surface S_(I) and an outerannular surface S_(O) that defines an inner diameter and a maximum outerdiameter, respectively. In the illustrated embodiment, the maximum outerdiameters of all five spoke rings 110 are equal. In alternativeembodiments, the maximum outer diameters of the spoke rings may vary.

In the illustrated embodiment, each spoke 112 extends from the innerannular surface S_(I) to the outer annular surface S_(O) of therespective spoke ring 110. The spokes 112 define openings O_(S) betweenone another. For illustrative purposes, the openings O_(S) are shown aspentagon-shaped. However, it should be understood that the openingsO_(S) may have any geometric shape. In an alternative embodiment (notshown), the spokes may form a more complex webbing rather than extendfrom the inner annular surface S_(I) to the outer annular surface S_(O).

Each spoke ring 110 has a stiffness k. As one of ordinary skill in theart would understand, the stiffness of a spoke ring may be defined by anumber of factors, including, without limitation, the material of thespoke ring and the geometry of the spokes and openings. Spoke rings witha higher stiffness are more resistant to deformation and compression. Inone embodiment, central spoke ring 110 a has a first stiffness k_(a),intermediate spoke rings 110 b each have substantially the same secondstiffness k_(b), and outer spoke rings 110 c each have substantially thesame third stiffness k_(c). In one embodiment, the second stiffnessk_(b) is greater than the first stiffness k_(a), and the third stiffnessk_(c) is greater than both the first stiffness k_(a) and the secondstiffness k_(b). In an alternative embodiment, the first stiffness k_(a)is greater than both the second stiffness k_(b) and the third stiffnessk_(c), and the second stiffness k_(b) is greater than the thirdstiffness k_(c). In another alternative embodiment, the second stiffnessk_(b) is greater than both the first stiffness k_(a) and the thirdstiffness k_(c), and the third stiffness k_(c) is greater than the firststiffness k_(a).

With continued reference to FIG. 1, the central spoke ring 110 a isshown as having a relatively lower number of spokes 112 a, with thespokes 112 a being separated by relatively larger openings O_(a). As oneof ordinary skill in the art would understand, this geometry wouldresult in a relatively low first stiffness k_(a). This low firststiffness k_(a) may be achieved by other means, such as with the use ofdifferent materials, construction methods, or geometries.

Intermediate spoke rings 110 b are shown as having more spokes 112 bthan central spoke ring 110 a. The spoke openings O_(b) of intermediatespoke rings 110 b are narrower than spoke openings O_(a) located withincentral spoke ring 110 a. Additionally, spokes 112 b of intermediatespoke rings 110 b are thicker than spokes 112 a of central spoke ring110 a. Both intermediate spoke rings 110 b have the same geometry andthe same stiffness k_(b). One of ordinary skill in the art wouldunderstand that this geometry would result in a relatively higherstiffness k_(b) than the central spoke ring stiffness k_(a).Alternatively, the intermediate stiffness k_(b) of spoke rings 110 b maybe achieved by other means, such as with the use of different materials,construction methods, or geometries for intermediate spoke rings 110 b.

Outer spoke rings 110 c are shown in FIG. 1 as having more spokes 112 cthan intermediate spoke ring 110 b, with spokes 112 c being separated byrelatively larger openings O_(c) than those of the intermediate spokering openings O_(b). In this embodiment, both outer spoke rings 110 chave the same spoke geometry, and the same stiffness k_(c). One ofordinary skill in the art would understand that the geometry of theouter spoke rings 110 c and the larger relative size of the outer spokering openings O_(c) would cause the outer spoke rings 110 c to have alower stiffness than intermediate spoke rings 110 b. Alternatively, thestiffness k_(c) of outer spoke rings 110 c may be achieved by othermeans, such as with the use of different materials, constructionmethods, or geometries for spoke rings 110 c.

In the illustrated embodiment, the five spoke rings 110 have threedifferent stiffnesses. In the illustrated embodiment, the intermediatespoke rings 110 b have the highest stiffness, and the central spoke ring110 a has the lowest stiffness. It should be understood that any numberof spoke rings having any number of different stiffnesses may beselected. After the stiffnesses of the spoke rings have been selected,the spoke rings are arranged in a desired manner, suitable to aparticular application. For example, the stiffness of each ring may beselected to produce a tire having desired characteristics, such as lownoise, low vibrations, or low rolling resistance.

When airless tire 100 is placed in contact with the ground in aload-bearing condition, airless tire 100 contacts the ground to form atire contact patch shape (not shown in FIG. 1). Because the airless tirecontact patch shape will be dictated by the stiffness of the spoke rings110, in addition to other factors, a design engineer can alter thecontact patch shape of the airless tire by varying the stiffness of thespoke rings 110 across the width of the airless tire. This could be doneto produce a curved leading edge of the contact patch shape that isdesirable when concerned with ride harshness and impact isolation.Further stiffness changes can be used to optimize the contact patchshape for off-highway tires, reducing soil compaction, a key designparameter for certain applications.

FIG. 1 depicts the spokes 112 of corresponding like spoke rings 110being arranged in alignment with one another. For example, the spokes112 c and openings O_(c) of each outer spoke ring 110 c are aligned witheach other, and the spokes 112 b and openings O_(b) of each intermediatespoke ring 110 b are aligned with each other. In an alternativeembodiment, the spokes 112 and openings O_(S) of corresponding likespoke rings are not in alignment with each other. It will be apparent toone of ordinary skill in the art that various alignments of spoke rings110 will cause airless tire 100 to have different performanceproperties. When spoke rings 110 are not aligned with each other, spokes112 of similar spoke rings 110 enter the contact patch shape area at adifferent time when airless tire 100 is rolling. The spoke rings 110 mayalso be aligned such that each spoke 112 of the all spoke rings 110enters the contact patch area at a different time when airless tire 100is rolling. One of ordinary skill in the art would be able to select analignment providing desired performance properties in any particularapplication.

After the spoke rings 110 are arranged in a desired manner, they areaffixed to a non-pneumatic hub (not shown), using known affixing means.Exemplary affixing means include, without limitation, welding, brazing,and the application of adhesive. A high annular strength band 114 isthen circumferentially attached about the spoke rings 110. The highannular strength band acts as a structural compression member on theairless tire 100, and increases interlaminar shear strength across theaxial length of the airless tire 100. As one of ordinary skill wouldunderstand, the high annular strength band 114 could include an elasticcenter portion, sandwiched between two inelastic outer portions, or becomposed of a single composite structure (see prior art U.S. Pat. No.5,879,484). The high annular strength band 114 may also be referred toas a “shear band” or “band.” In an alternative embodiment, the highannular strength band may be omitted.

A tire tread 116 is then wrapped about the high annular strength band114. The tire tread 116 may include elements, such as ribs, block, lugs,grooves, and sipes as desired to improve the performance of the tire invarious conditions.

FIG. 2 shows a cross-section of airless tire 100. As can be seen fromthis view, each spoke ring 110 of airless tire 100 has the samethickness S_(T). In alternative embodiments (not shown), the spoke ringthickness of spoke rings may vary. By varying thicknesses S_(T), thecontact patch shape created by airless tire 100 may be adapted to suit awide range of applications, including agricultural and passengerapplications.

FIG. 3 illustrates a cross section of an alternative embodiment of anairless tire 200. In this embodiment, spoke rings 210 have differentmaximum outer diameters and different stiffnesses k. The spoke rings 210in this embodiment have inner diameters D_(I) that are substantially thesame. Each spoke ring 210 may have a unique stiffness k, or may have acommon stiffness k with one or more other spoke rings 210. In thisembodiment, central spoke ring 210 a has a first stiffness k_(a),intermediate spoke rings 210 b each have a second stiffness k_(b), andouter spoke rings 210 c each have a third stiffness k_(c). In oneembodiment, the first stiffness k_(a) is lower than both the secondstiffness k_(b) and the third stiffness k_(c). Additionally, the secondstiffness k_(b) is lower than the third stiffness k_(c). In analternative embodiment, the first stiffness k_(a) is greater than boththe second stiffness k_(b) and the third stiffness k_(c), and the secondstiffness k_(b) is greater than the third stiffness k_(c). In anotheralternative embodiment, the second stiffness k_(b) is greater than boththe first stiffness k_(a) and the third stiffness k_(c), and the thirdstiffness k_(c) is greater than the first stiffness k_(a).

Each spoke ring 210 may have a unique outer diameter, or may have acommon outer diameter with one or more other spoke rings 210. In theillustrated embodiment, central spoke ring 210 a has a first maximumouter diameter D_(a), intermediate spoke rings 210 b each have a secondmaximum outer diameter D_(b), and outer spoke rings 210 c each have athird maximum outer diameter D_(e). The first maximum outer diameterD_(a) is greater than the second maximum outer diameter D_(b), which inturn is greater than the third maximum outer diameter D_(c). It shouldbe understood that any number of spoke rings having any number ofdifferent outer diameters may be employed. After the outer diameters ofthe spoke rings have been selected, the spoke rings are arranged in adesired manner, suitable to a particular application. For example, theouter diameter of each ring may be selected to produce a tire havingdesired characteristics, such as low noise, low vibrations, or lowrolling resistance.

Use of variable diameter spoke rings allows for a curved or toroidalband (or shear band) to be used in this type of non-pneumatic tire(“NPT”) design. The toroidal band allows additional deflection needed tomaximize tire contact patch area. This is especially important foroff-highway or agricultural tires which need a contact patch shape witha greater area to minimize soil compaction.

In the illustrated embodiment, each spoke ring 210 has a constant outerdiameter. In alternative embodiments (not shown), the spoke rings mayhave variable outer diameters. For example, the outer diameter of eachspoke ring may vary in the axial direction, such that when the spokerings are assembled, the assembly has a smooth, curved outer surface.

Each spoke ring 210 may have a unique thickness, or may have a commonthickness S_(T) with one or more other spoke rings 210. Tread 214 iswrapped around the outer surfaces of spoke rings 210. In an alternativeembodiment (not shown), a high annular strength band is disposed betweenthe outer surfaces of the spoke rings and the tread.

FIG. 4 illustrates a cross section of another alternative embodiment ofan airless tire 300. The tire 300 is substantially similar to the tire200 discussed above, except for the differences identified below.

In this embodiment, each spoke ring 310 has concave portions 312 andconvex portions 314 that alternate along the sides of spoke rings 310.When aligned, the concave portions 312 and convex portions 314 ofadjacent spoke rings 310 abut each other, as seen in FIG. 4. Thisconfiguration may provide increased rigidity and support among the spokerings 310. Alternatively, spoke rings 310 may include other structuresthat adjoin to one another, such as protrusions in one spoke ring anddepressions to receive the protrusions in another spoke ring. Tread 316circumferentially surrounds spoke rings 310.

FIG. 5 illustrates a perspective view of yet another alternativeembodiment of an airless tire 400. In the illustrated embodiment, theairless tire 400 has a single wheel portion 410. Wheel portion 410 maybe a single unitary structure, or may be made up of a plurality of spokerings 110 fused together. Wheel portion 410 has a webbing 412 instead ofspokes that extend from an inner annular surface to an outer annularsurface. The webbing 412 may be any pattern or shape sufficient toprovide support. The maximum outer diameter W_(D) of wheel portion 410may vary along an axial direction. For example, the maximum outerdiameter may be greater in an equatorial plane and smaller towards thesides of airless tire 400.

The stiffness k of the webbing portion 412 may vary along an axialdirection of wheel portion 410. A varying stiffness k throughout wheelportion 410 can be achieved in several ways. In one embodiment, severalspoke rings 110 having various stiffnesses k are fused together. In analternative embodiment, different materials are used in the wheelportion 410 during manufacture to create pre-stresses within the wheelportion. In another alternative embodiment, the webbing has varyinggeometry in an axial direction, which causes the stiffness to vary inthe axial direction. The webbing geometry may be varied through moldingor machining processes, or by a 3D printing or additive manufacturingprocess. Those of ordinary skill in the art will understand that othermethods known in the art may be used to provide a varying axialstiffness within wheel portion 410.

In the embodiment shown in FIG. 5, non-pneumatic hub 414 is affixed tothe center of webbing 412 using known affixing means. Exemplary affixingmeans include, without limitation, welding, brazing, and the applicationof adhesive. Non-pneumatic hub 414 can be attached to a vehicle in asimilar manner as a wheel in a conventional tire. In other embodiments,additional webbing 412 can be used instead of non-pneumatic hub 414.

The spoke rings and webbing disclosed in the embodiments of FIGS. 1-5may cause the airless tire 100, 200, 300, 400 to form a rounded contactpatch shape when in contact with the ground. The rounded contact patchshape reduces the effects of road impact and noise. The curvature of therounded contact patch shape can be determined by various factors,including, without limitation, each spoke ring's stiffness, outerdiameter, thickness, spoke geometry, number of spokes, shape and numberof openings, and the number of spoke rings included in airless tire. Byvarying these parameters, the airless tire may be adapted to suit a widerange of applications, including agricultural applications and passengervehicle applications. For example, in some applications such as use inagricultural vehicles, uniform contact pressure and maximized contactarea may be desired. An airless tire with a rounded contact patch shape(or rounded band) can be designed to deflect more at low loadsmaximizing contact area and minimizing soil compaction. An airless tirewith flat contact patch shape loses the ability to deflect in the radialdirection at different rates across its axial width which will causeless deflection, and less contact patch area, especially at light loadconditions. An airless tire with a rounded contact patch shape willresult in superior (reduced) soil compaction performance and superior(reduced) ride harshness for the driver/operator.

FIG. 6 depicts an exemplary elongated rounded contact patch shape 500which is formed when one of the airless tires 100, 200, 300, 400 is incontact with a rolling surface in a load bearing condition. Elongatedrounded contact patch shape 500 includes a rounded leading edge 512 anda rounded trailing edge 514. The axial stiffness distribution or varyingaxial diameter of the airless tires 100, 200, 300, 400 contribute to theforming of rounded edges 512 and 514.

By contrast, FIG. 7 depicts a contact patch shape 600 of a prior artairless tire (not shown). The contact patch shape 600 includes straightleading and trailing edges 612, 614. An airless tire making a flatcontact patch shape 600 results in greater ride vibration and noise thanan airless tire making a rounded contact patch shape 500.

The contact patch shape is formed when the airless tire is in contactwith a rolling surface in a load bearing condition. As one example, FIG.8 is a schematic drawing depicting a side view of the airless tire 100of FIGS. 1 and 2 bearing a load. In one embodiment, the effects of usingvariable stiffness rings in axial alignment can be enhanced based on theload distribution within the airless tire. The load carryingdistribution in such an embodiment can rely more heavily on loadtransmitted in compression through the spokes at the bottom of the tire(between the load and the ground surface), and less on the shear band totransfer load to the top of the tire. In some NPTs the load is carriedprimarily through the use of a cylindrical shear band with spokes thatbuckle at the bottom of the tire. These NPTs are considered “toploaders” and carry most of the load through the shear band and the upperspokes in tension. Other NPTs are essentially rigid (or semi-flexible)structures that carry a majority of the load through the bottom portion,“bottom loaders.” In one embodiment, the load is relatively balancedbetween the spoke rings and shear band such that approximately 50% ofthe load is carried through the bottom spokes in compression andapproximately 50% of the load is carried through the shear band andupper spokes in tension. This approximate 50/50 load distribution allowsfor varying the diameters and stiffness of the spoke rings to create adesired contact patch shape. In this embodiment, the spokes 112undergoing a compressive force do not buckle when airless tire 100 isloaded.

The airless tire 100 creates a rounded contact patch shape 500 on arolling surface when a load is placed on airless tire 100. Roundedleading edge 512 is formed when airless tire 100 undergoes a loadingforce. Rounded leading edge 512 result in reduced ride vibration andnoise by allowing the tire to pass over bumps in the road more softlythan an airless tire with a straight leading edge.

To the extent that the term “includes” or “including” is used in thespecification or the claims, it is intended to be inclusive in a mannersimilar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed (e.g., A or B) it is intended to mean “Aor B or both.” When the applicants intend to indicate “only A or B butnot both” then the term “only A or B but not both” will be employed.Thus, use of the term “or” herein is the inclusive, and not theexclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into”are used in the specification or the claims, it is intended toadditionally mean “on” or “onto.” Furthermore, to the extent the term“connect” is used in the specification or claims, it is intended to meannot only “directly connected to,” but also “indirectly connected to”such as connected through another component or components.

While the present application has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the application, in its broaderaspects, is not limited to the specific details, the representativeapparatus and method, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

What is claimed is:
 1. An airless tire, comprising: a plurality of spokerings, including a first spoke ring adjacent to a second spoke ring,wherein each of the plurality of spoke rings includes an annular outersurface, an annular inner surface, and a plurality of spokes extendingbetween the outer and inner surfaces, wherein the first spoke ring has afirst stiffness and the second spoke ring has a second stiffnessdifferent from the first stiffness; and a tread layer extendingcircumferentially around the annular outer surfaces of the plurality ofspoke rings.
 2. The airless tire of claim 1, wherein the spoke rings areattached to a hub, and wherein when a load is applied to the hub, thespokes positioned below the hub are compressed and the spokes positionedabove the hub are tensioned.
 3. The airless tire of claim 2, wherein thetension and compression forces are approximately equal in magnitude. 4.The airless tire of claim 1, further comprising a shear band disposedabout the outer annular surfaces of the spoke rings.
 5. The airless tireof claim 1, wherein the tire forms a contact patch shape with a roundedleading edge when a load is applied to the tire.
 6. The airless tire ofclaim 1, wherein the first spoke ring has a first maximum outer diameterand the second spoke ring has a second maximum outer diameter differentfrom the first maximum outer diameter.
 7. The airless tire of claim 1,further comprising a third spoke ring, wherein the third spoke ringincludes a plurality of spokes, and wherein the spokes of the thirdspoke ring are not aligned with the spokes of the first spoke ring alongan axis of rotation of the airless tire.
 8. The airless tire of claim 1,wherein the spoke rings are made from a material selected from the groupconsisting of corded carbon-filled rubber, nylon, polyester, glass oraramid fibers with resin, thermoplastic, and urethane.
 9. A tire,comprising: a wheel portion having an axis of rotation, wherein thewheel portion includes an annular outer surface, and wherein a distancebetween the axis of rotation and the annular outer surface varies alongan axial direction; and a webbing extending from an annular innersurface of the wheel portion towards the axis of rotation, wherein astiffness of the webbing varies along the axial direction.
 10. The tireof claim 9, further comprising a shear band attached to the outerannular surface of the wheel portion, and wherein the webbing in a lowerregion of wheel portion is compressed and the webbing in an upper regionof wheel portion is tensioned by the shear band when a load is placed onthe tire.
 11. The tire of claim 10, wherein the compression and tensionforces are approximately equal in magnitude.
 12. The tire of claim 9,wherein the webbing is attached to a hub in the center of the tire. 13.The tire of claim 9, wherein the wheel portion and webbing comprise aplurality of spoke rings.
 14. The tire of claim 9, wherein the tireforms a contact patch shape with a rounded leading edge.
 15. The tire ofclaim 9, wherein the webbing is made from a first material having afirst stiffness and a second material different from the first material,the second material having a second stiffness different from the firststiffness.
 16. A non-pneumatic tire, comprising: a plurality of spokerings, including a first spoke ring disposed between a second spoke ringand a third spoke ring, wherein each of the plurality of spoke ringsincludes an annular outer surface, an annular inner surface, and aplurality of spokes extending between the outer and inner annularsurfaces, wherein the first spoke ring has a first stiffness, the secondspoke ring has a second stiffness different from the first stiffness,and the third spoke ring has a third stiffness approximately equal tothe second stiffness; and a tread portion covering an outer surface ofthe plurality of spoke rings.
 17. The non-pneumatic tire of claim 16,wherein the first spoke ring has a first spoke region having a firstthickness and a second spoke region having a second thickness, the firstthickness being greater than the second thickness, wherein the secondspoke ring has a third spoke region with a third thickness and a fourthspoke region with a fourth thickness, the third thickness being greaterthan the fourth thickness, wherein the first spoke region abuts thefourth spoke region, and wherein the second spoke region abuts the thirdspoke region.
 18. The non-pneumatic tire of claim 16, wherein the firstspoke ring has a first maximum outer diameter, the second spoke ring hasa second maximum outer diameter different from the first maximum outerdiameter, and the third spoke ring has a third maximum outer diameterthat is approximately equal to the second maximum outer diameter. 19.The non-pneumatic tire of claim 16, further comprising a shear bandattached to the outer annular surfaces of the spoke rings, whereinspokes in lower regions of spoke rings compress and spokes in upperregions of spoke rings are tensioned by the shear band when a load isplaced on the non-pneumatic tire.
 20. The non-pneumatic tire of claim19, wherein the compression and tension forces are approximately equalin magnitude.